1. Field of the Invention
The present invention relates to a voltage measurement apparatus for measuring, under insulative conditions, the voltage of each of a plurality of power sources connected in series. More particularly, the present invention relates to a voltage measurement apparatus suited to measuring the voltage of each cell in a high-voltage battery including a plurality of cells connected in series, in which the battery is used as a power source in an electric vehicle, such as a HEV (hybrid electric vehicle).
2. Description of the Related Art
A high-voltage battery, which is used as a power source in a HEV, includes a number of cells connected in series so as to obtain a high voltage. For such a high-voltage battery, abnormal conditions, the state of charge, and the like are preferably detected by measuring the voltage of each cell. However, since a high-voltage battery uses a number of cells, it is not easy to measure the voltage of every cell. Typically, a number of cells connected in series are grouped into a plurality of battery modules each including a predetermined number of cells, and the voltage of each battery module is then measured.
Further, an attempt is typically made to simplify the configuration of the measurement circuit for measuring the voltage of each battery module, in which all battery modules are sequentially connected via a switching circuit to a single voltage measurement circuit and the voltage of each battery module is measured sequentially.
A high-voltage battery used as a power source in a HEV is mounted on the HEV while being insulated from the chassis in order to avoid danger. Therefore, a voltage measurement apparatus measures the absolute voltage of each battery module in the high-voltage battery. In contrast, a control system, which controls charge and discharge of a high-voltage battery, uses the potential of a chassis as a reference potential.
Japanese Laid-Open Publication No. 11-248755 discloses a voltage measurement apparatus having a simple circuit configuration which measures the voltage of each battery module in a high-voltage battery including a plurality of cells connected in series. In this apparatus, a switching circuit including a combination of two multiplexers is used, and the voltage of each battery module is sequentially applied to a provided condenser, corresponding to each battery module. Further, all of the condensers are sequentially connected to a single voltage measurement circuit.
The above-described voltage measurement apparatus can measure the voltage of each battery module with high precision, in which the number of expensive analog switches used in a switching circuit can be significantly reduced, thereby simplifying the overall circuit configuration, and increasing economy.
In a high-voltage battery used in a HEV, the voltage of each of a plurality of battery modules is constantly measured at predetermined times during the time when the HEV is driven. In this case, during the time when the HEV is driven, a current flowing through each module varies from moment to moment. Therefore, the voltage value of each battery module varies depending on the time when the voltage measurement is conducted. In extreme cases, when charge and discharge of a high-voltage battery are switched, the current value of each battery module may be dramatically changed.
As described above, the current value of each battery module varies depending on the time when the voltage measurement is conducted. In this case, the voltage measurement apparatus disclosed in the above-described publication, or the like is unlikely to accurately measure the voltage of each battery module. As a result, the measured voltage of each battery module is inaccurate, which leads to an error in detection of an abnormal battery, a reduction in control precision of charge and discharge, or the like.
According to an aspect of the present invention, a voltage measurement apparatus for measuring a voltage of each of N power sources connected in series, includes N capacitance elements provided respectively corresponding to the N power sources, and connected in series, a first switching section for simultaneously applying a voltage of each power source to one of the N capacitance elements corresponding to said power source, a voltage measurement section for measuring a voltage of each capacitance element, and a second switching section for sequentially connecting each capacitance element to the voltage measurement section.
In one embodiment, the first switching section includes two sampling switches provided between terminals of a circuit including the N power sources connected in series, and corresponding terminals of a circuit including the N capacitance elements connected in series, and Nxe2x88x921 sampling switches, each provided between an interface portion between a corresponding pair of power sources connected in series, and an interface portion between a corresponding pair of capacitance elements connected in series. The N+1 sampling switches are simultaneously switched ON or OFF.
In one embodiment of this invention, the second switching section includes a first multiplexer including a switch connected between a positive-side terminal of each odd-numbered capacitance element of the N capacitance elements connected in series, and one of a pair of input terminals of the voltage measurement section, and a second multiplexer including a switch connected between a positive-side terminal of each even-numbered capacitance element of the N capacitance elements connected in series, and the other of the pair of input terminals of the voltage measurement section. One of the switches in each multiplexer is simultaneously selected and switched ON or OFF in such a manner that the N capacitance elements are sequentially connected to the voltage measurement section.
In one embodiment of this invention, the voltage measurement section is connected to a polarity correction section for inverting a polarity of a voltage to be measured.
In one embodiment of this invention, the each capacitance element includes a pair of capacitance sub-elements. The voltage measurement section is of a differential input type. The second switching section includes a third multiplexer for selectively connecting an intermediate connecting point between the pair of capacitance sub-elements connected to the voltage measurement section to a reference potential of the voltage measurement section.
In one embodiment of this invention, each sampling switch in the first switching section includes a semiconductor relay element for driving a MOS transistor using a light signal.
In one embodiment of this invention, each switch in the second switching section includes a semiconductor relay element for driving a MOS transistor using a light signal.
Thus, the invention described herein makes possible the advantages of providing a voltage measurement apparatus capable of measuring the coincident voltages of all of a plurality of power sources connected in series, without the influence of variations in the current value.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.